1 /* origin: FreeBSD /usr/src/lib/msun/src/e_logf.c */
3 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
6 * ====================================================
7 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
9 * Developed at SunPro, a Sun Microsystems, Inc. business.
10 * Permission to use, copy, modify, and distribute this
11 * software is freely granted, provided that this notice
13 * ====================================================
20 ln2_hi
= 6.9313812256e-01, /* 0x3f317180 */
21 ln2_lo
= 9.0580006145e-06, /* 0x3717f7d1 */
22 /* |(log(1+s)-log(1-s))/s - Lg(s)| < 2**-34.24 (~[-4.95e-11, 4.97e-11]). */
23 Lg1
= 0xaaaaaa.0p
-24, /* 0.66666662693 */
24 Lg2
= 0xccce13.0p
-25, /* 0.40000972152 */
25 Lg3
= 0x91e9ee.0p
-25, /* 0.28498786688 */
26 Lg4
= 0xf89e26.0p
-26; /* 0.24279078841 */
30 union {float f
; uint32_t i
;} u
= {x
};
31 float_t hfsq
,f
,s
,z
,R
,w
,t1
,t2
,dk
;
37 if (ix
< 0x00800000 || ix
>>31) { /* x < 2**-126 */
39 return -1/(x
*x
); /* log(+-0)=-inf */
41 return (x
-x
)/0.0f
; /* log(-#) = NaN */
42 /* subnormal number, scale up x */
47 } else if (ix
>= 0x7f800000) {
49 } else if (ix
== 0x3f800000)
52 /* reduce x into [sqrt(2)/2, sqrt(2)] */
53 ix
+= 0x3f800000 - 0x3f3504f3;
54 k
+= (int)(ix
>>23) - 0x7f;
55 ix
= (ix
&0x007fffff) + 0x3f3504f3;
68 return s
*(hfsq
+R
) + dk
*ln2_lo
- hfsq
+ f
+ dk
*ln2_hi
;